The purpose of this work is to determine the manner in which certain fungal fatty acids are transformed into oxygenated cyclopentane- containing metabolites. Brefeldin A and jasmonic acid biosynthesis will be studied in detail in order to compare the cyclization mechanism with that of the prostaglandins. Cultures will be exposed to an 18 O2, 16 O2 atmosphere to determine the origin of the oxygen atoms. The sequence of transformations from fatty acid to metabolite will be determined by feeding labelled potential intermediates and observing specific incorporation. The details of the cyclization process will be examined by using specifically tritiated precursors. The enzymes involved will then be fractionated and the co-factor requirements determined. This information will be used to guide substrate specificity studies which have the goal of converting unnatural substrates into fermentation products which are potential starting materials for the synthesis of prostaglandins.